1. Technical Field
The invention concerns a superimposed transmission for driving a rotational speed-variable work machine having the following design:
an input shaft is connected to an intermediate shaft;
a pump wheel of a hydrodynamic converter rotates with the intermediate shaft;
a turbine wheel of the hydrodynamic converter rotates with a superposition means; and
an intermediate shaft and the transmission means are connected to an output shaft by means of a differential gear.
Superimposed transmissions where a rotation speed which is applied to the output shaft via input shaft and intermediate shaft is superimposed to a second rotation speed, which is coupled out via a hydrodynamic converter and then again coupled via a matching differential gear, are substantially disclosed in the state of the art.
It may be referred for instance to the disclosure of AT-PS 275 988 or DE 34 41 877 A1. Document DE 44 22 444 A1 shows such a force-transmitting unit for driving a rotational speed-variable work machine. The unit consists of an input shaft, an output shaft by means of a hydrodynamic converter, including pump wheel, turbine wheel and guide wheel. The hydrodynamic converter is arranged coaxially with a differential gear and an output transmission member of the differential gear is permanently coupled with the output shaft.
In the state of the art, hollow shafts are employed as a transmission means between the coupling out via the hydrodynamic converter and the actuation of the differential gear. These hollow shafts, which are typically designed as rotating coaxial drums, hence exhibit the shortcoming that they are quite heavy, have a high moment of inertia and render access to the elements arranged in the hollow shaft significantly more difficult. Hence, the structure of a particularly compact transmission is finally influenced negatively by the hollow shafts.
For further reference to the state of the art, documents U.S. Pat. No. 2,834,228 A as well as FR 1 226 770 A may prove useful.
It is then an object of the present invention to avoid the shortcomings in the above mentioned state of the art and to make an optimised superimposed transmission with simple, compact and maintenance friendly structure available.
2. Description of the Related Art
The object of the invention is met in that with a superimposed transmission of the type above mentioned, the transmission means are designed as at least two coupling shafts which connect the turbine wheel of the hydrodynamic converter to the differential gear whereas said at least two coupling shafts run parallel to the intermediate shaft.
The solution provided by the invention thus provides that the transmission means are designed as at least two coupling shafts instead of one hollow shaft or rotating drums. Said at least two coupling shafts then connect the turbine wheel of the hydrodynamic converter to the differential gear, which is ideally designed as a planetary gear. Said at least two coupling shafts run parallel to the intermediate shaft and transfer the coupled out rotation speed, which is then superimposed symmetrically in the differential gear again to the rotation speed transmitted directly from input to output via the intermediate shaft. Consequently, the rotation speed of the output shaft can be influenced accordingly as in the older as well as similar common superimposed transmissions. In the sense of the present invention, by each parallel coupling shaft is meant a shaft whose rotational axis runs parallel or, to be more accurate, within the usual tolerances parallel to the rotational axis of the intermediate shaft. The rotational axes also lie spaced apart parallel close to one another and are never identical as they were arranged in the concentric structure of the intermediate shaft and of the hollow shaft surrounding said shaft according to the state of the art.
By ruling out a large hollow shaft, quite complex to control from a mechanical viewpoint, which according to the structure of the transmission reaches a comparatively large diameter and hence has matching great sizes, a simplified structure can now be obtained using said at least two coupling shafts. Also the accessibility of the elements which were arranged previously in the region of the hollow shaft, may now be significantly facilitated for assembly and maintenance work, since they are situated close to the coupling shaft and are consequently easily accessible.